Light-weight gypsum product



6. COMPOSITIONS,

COATING OR PLASTIC.

- "was. "in

UNITED STATES PATENT OFFICE.

HARRY E. BROOKBY, OF EVANSTON, ILLINOIS, ASSIGNOR TO UNITED STATES GYPSUM COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

LIGHT-WEIGHT No Drawing.

This invention relates to improvements in building material and more particularly to the production of a light weight plaster board and the method of making same.

Plaster board having a plaster body with fibrous cover sheets adhering to the flat faces has been used for a long time in the building trade as a substitute for wooden or metal lath and more recently the improvements in plaster board have produced a plaster wallboard which in effect is a factory made plaster wall and there is a demand all over the country for the plaster wallboard that when nailed to the studding of the building is ready for decoration and which provides a fireproof wall that remains uniform under all changes in temperature or atmospheric conditions, that is, it does not warp or buckle nor does it shrink or crack after it has been erected.

This plaster board and plaster wallboard is made in standard widths and thicknesses and cut in desired lengths and weighs between 1,850 and 2,000 pounds per thousand square feet. The gypsum from which these boards are made is a natural deposit and is found only in certain sections of this country and, on account of the nature of the mineral, plaster board plants are usually located at or near the gypsum mines with the result that it is necessary to transport the plaster board great distances to supply the demand in territories where there are no gypsum deposits and on account of the weight increases the cost considerable to the users in such territories.

It is an object of this invention to reduce the weight of the plaster body of plaster board and wallboard while at the same time maintaining the other high standardized qualities. The commercial advantages of such an improvement are obvious as well as the advantage to the purchasing public.

Since this invention relates to the composition of the body of the plaster board and may be applied to any of the well known plaster boards now on the market which are universally produced by well known machines in which a fibrous cover sheet is advanced, the plaster body in a plastic state deposited upon the advancing cover sheet, a top fibrous cover sheet applied over the plastic mass and the two cover sheets with the plastic body passed through a board GYPSUM PRODUCT.

Application filed August 19, 1922. Serial No. 583,040.

forming device comprising a pressure roller that imparts the desired thickness to the board and then carried in a continuous strip upon a conveyor a great enough distance to allow the plastic body to set sufficiently to be cut into the desired lengths at the end of the conveyor, removed and transported to the drying kilns, it is not necessary to illustrate or describe such a machine in more specific detail, yet it is to be understood that minor detail changes, such as in the preferred proportions of the ingredients employed in carrying out this invention, may be made without departing from the scope thereof.

The plastic mass forming the plastic body deposited upon the cover sheet as above described is calcined sum or laster of Pal-1s mixed with \Yaier anil usuaIly wood fibre or other aggregate, generally mecliamquite extended and voluminous and, in suspension, displaces a corresponding volume .of the heavier plastic calcined gypsum. In

other words, the mixture at this stage substantialy comprises, on the one hand, a large number of suspended dispersed gelatinous particles of the gypsum-casein reaction product, and, on the other hand, suspended particles of plaster of Paris. When using casein in the the proportion hereinafter specified and in the manner described, the plaster board formed as a result of the bulkier mass of the gypsum casein compound is 20 to 25 per cent lighter in weight than the usual plaster board, and is more pliable than if the casein had not been employed.

The stock solution is preferably made by first soaking commercial granulated casein in water in the pro ortion of about a to o omcasein to Emu o or u l l y one hour with the water near the boiling point, wh1ch softenrtire'case' after which one quarter t g o ng l 1 alf ounce o f strong. .liquidfammonfumdrydroiiillfor each 5 to 6 ounces of casein is added and stiiflzd untifilieci'eifi'gbEs into clear sol"- tioTiw. 'It is preferable", in order to keep the wall board safely pliable, to add to the mix of calcined gypsum, water and aggregate on the mixing and conveying belt before depositing on the board forming machine the above described casein stock solution. I have found that very satisfactory results may be obtained by using substantially onehalf ounce of casein to ten square feet of wall board or 0.33 cu. ft. of core volume of wall board. As casein compounds have a tendency to retard the set of calcined gypsum with water it is preferable to add a positive accelerator such as commonly used or t is purpose, 0 avoid slowing down the board production.

The improved board made with this type of body is very strong due to the increased strength imparted to the porous body by the cementing action of the calcium-casein compound, and is about 25 per cent lighter in weight per uare foot than the ordinary gypsum boar s of similar thickness, weighing between 1250 to 1350 pounds per thousand square feet. By regulating or varying the amount of casein solution added to the mixture, and thereby controlling the amount of gypsum casein suspension compound, the weight of the board can be varied to meet the desired structural and shipping conditions.

The body of calcined gypsum mixed with calcium caseinate bonds the fibrous cover sheets to it as well in the calcined gypsum boards and such boards when dried is more water resistant than the ordinary gypsum board. While I have described my invention in connection with the production of light-weight plaster board, it is obvious that it is equally applicable to the preparation of other light weight gypsum products such as tile, blocks and other cast or molded gypsum articles.

The application of this invention to a gypsum block or tile is described in my copending application Serial No. 584,342, filed Au st 25, 1922.

aving thus described one method of successfully carrying out my invention, and without limitinglm self to the recise procedure herein 'sc osed, what claim as new and desire to be protected by Letters Patent of the United States is:

1. A dried light-weight cellular gypsum product comprising hydrated plaster of Paris as the major ingredient, and voids left by the contraction and drying of calcium caseinate contained therein.

2. A dried light-weight cellular gypsum product comprising hydrated plaster of Paris as the major ingredient, and voids produced by the contraction and drying of agypsum and casein reaction product produced in said mass.

.3. A lightweight cellular product comprising set plaster of Paris as the major ingredient and the dried reaction product of calcined hydrated gypsum and casein in solution, the casein being present in the proportion of substantially one-half ounce to substantially 0.33 cu. ft. of the entire product.

4. The method of producing numerous small voids in a set which comprises ad ing to a slurry of calcined gypsum and water an aqueous solution of ammonium caseinate in such an amount that voids Will be formed when allowing the mass to set, harden and dry.

5. The process of producing 'a dried lightplaster of Paris product weight gypsum product which comprises making a plastic mass of calcined gypsum and water as the major ingredient, then producing a suspension of a 'ypsum casein reaction compound therein by adding to' said major ingredient an aqueous solution of casein thus forming a composite mass which is allowed to set, harden and dry, the said casein solution being added in such reacting proportions with the major ingredient that a multitude of small dispersed voids results during the drying process and remain in the finished gypsum product. I

6. The process of producing a light weight gypsum product which comprises making a plastic mass of calcined gypsum and water, then precipitating calcium caseinate therein by adding to said plastic calcined gypsum mass an aqueous solution of casein and ammonium hydroxide, said casein solution being proportioned substantially at the rate of one-half ounce of casein to substantially 0.33 cu. ft. of the composite mass, and then permitting the mass to set, harden and dry. 

